Cubic Regression


The cubic regression option finds the equation of a cubic equation of the form y = ax3 + bx2 + cx + d that best fits a set of data. First, press to enter the data .



Press to view the statistics calculation options.



Press



Enter the columns to be used for the x and y entries, c1 and c2 in this case. The regression equation can be automatically stored in the equation editor by selecting the Stor RegEQ.



Therefore, the best-fit cubic equation for this data is approximately y = 0.03x3 - 0.11x2 -0.89x -0.47.


Note: The resulting cubic equation is an exact fit if four non collinear, non parabolic data points are entered.

The TI-89 does not calculate the correlation coefficient r. It does calculate the coefficient of determination, r2.